1. Field of the Invention
The present invention relates to a pressure-reducing valve for regulating the pressure of a fluid supplied from a primary side into a predetermined lower pressure and discharging the fluid under the regulated pressure to a secondary side.
2. Description of the Related Art
Heretofore, there have been known pressure-reducing valves for regulating the pressure of a fluid supplied from a primary source such as a fluid pressure supply into a predetermined lower pressure and discharging the fluid under the regulated pressure to a secondary device such as a fluid pressure actuator.
One conventional pressure-reducing valve is shown in FIG. 5 of the accompanying drawings. As shown in FIG. 5, the pressure-reducing valve, generally denoted by the reference numeral 1, is of the pressure relief type and basically comprises a casing 2 and a bonnet 3. The casing 2 and the bonnet 3 jointly define a space or chamber 4 which houses a diaphragm 5 supporting a relief valve mechanism 6 centrally thereon.
The relief valve mechanism 6 has a relief valve seat 9 mounted on a lower surface of the diaphragm 5 and having a relief passage 8 defined therein which is sealed by an upper end of a stem 7. The relief passage 8 comprises a vertical through hole. The upper end of the stem 7, which is of a hemispherical shape, is normally seated on a lower open end of the relief passage 8 to close the same for thereby sealing the relief passage 8.
The relief valve mechanism 6 also includes a diaphragm holder 10 which holds the diaphragm 5 between itself and the relief valve seat 9, and a nut 11 threaded over an upper end portion of the relief valve seat 9 and joining the relief valve seat 9 and the diaphragm holder 10 to each other. The bonnet 3 has a relief port 12 for releasing the secondary-side pressure of a fluid in excess of a predetermined pressure setting from the chamber 4 into the atmosphere.
The relief valve mechanism 6 operates as follows: When the secondary-side fluid pressure becomes higher than the predetermined pressure setting, the diaphragm 5 is elevated, lifting the relief valve seat 9 off the upper end of the stem 7. The fluid under the increased fluid pressure flows through the relief passage 8 into the chamber 4, and is then discharged through the relief port 12 into the atmosphere, whereupon the secondary-side fluid pressure is maintained at the predetermined pressure setting.
The relief valve mechanism 6 of the conventional pressure-reducing valve 1 is disadvantageous in that the relief valve seat 9 and the stem 7 tend to be tilted or misaligned with respect to each other because of limited dimensional accuracy of the stem 7 and limited accuracy with which the relief valve mechanism 6 is assembled. If the relief valve seat 9 and the stem 7 are tilted or misaligned with respect to each other, then the relief passage 8 is not sufficiently sealed and hence its through hole is not fully closed, allowing part of the secondary-side fluid to leak through the relief passage 8 and the relief port 12 into the atmosphere.